1. Field of the Invention
The present invention relates generally to refractory insulation mounting systems, energy-efficient systems for minimizing heat loss from such devices as high temperature furnaces used in the steel industry. Features of the invention have particularly advantageous application to a furnace door opening of a slab re-heat furnace, and are described in the environment of an exit door opening of a furnace of this type. Features of the present invention relate specifically to insulated furnace doors, and to methods for their manufacture, rebuilding and repair.
2. Prior Art
It is customary to line the walls of high temperature furnaces with refractory material to protect the furnace walls and other and structural elements against the debilitating effects of high temperature, and to minimize heat loss. The most commonly used refractory material is heavy, brittle ceramic. The weight and brittle character of this material renders it unsuitable for use on furnace doors which require frequent movement and are subject to shocks and stresses.
Furnace doors typically have been lined with relatively light, flexible refractory materials such as fibrous alumina-silica composites. These materials have been compacted to form lightweight blankets, pads or batts having handling characteristics resembling those of felt fabrics. When a thick layer of refractory insulation has been required, say 8 to 10 inches, various approaches have been tried in efforts to utilize these fibrous refractories. In some cases, blankets or batts of fibrous refractories have been applied in layered arrays using temperature-resistant adhesives. However, the mechanical strength of these fibrous refractory materials is quite low, and the exposed layers tend to slough off gradually, or to be torn away during use. Some installations utilize anchor pins which impale the layers to hold them in place, but these can readily tear through the refractory layers, and the pins tend to deteriorate as the result of exposure to the furnace heat.
Another approach to installing fibrous refractory materials has been to form the material into modules of a predetermined size. In this case, one or more blankets of fibrous refractory are folded in an accordian-like manner to produce a block of insulation material, with parallel planes of the folds extending normal to the plane of a furnace door or other furnace wall surface on which the block is to be mounted. The block, thus formed, is compressed and banded until installation. Various types of fastening devices have been suggested for mechanically attaching these blocks to wall structures in tight contact with each other, but the proposed means of attachment have been unduly complex, time-consuming to use, and have not provided the desired type of connection needed for long service under conditions of significant heat and mechanical stress.
Furnace walls and doors which have been insulated in accordance with present-day practice deteriorate rapidly under the intense heat and mechanical shock conditions to which they are often subjected. By way of example, the exit doors on a steel slab reheat furnaces presently require rebuilding with complete replacement of the refractory material at about six month intervals. This is a costly procedure, and it is important to reduce its frequency. Ideally, door life can be increased to at least about eighteen months to correspond with the normal "campaign" life of a furnace, at the end of which time the furnace is shut down and thoroughly serviced.